Small internal combustion engines are used in a wide variety of applications including for example, lawn mowers, lawn tractors, snow blowers and power machinery. Commonly, such internal combustion engines employ a carburetor to provide an appropriate air-fuel mixture to the combustion chamber of the internal combustion engine for generating power. Frequently, such carburetors have a fuel bowl that is coupled to a narrow throat/venturi region of the carburetor that serves as the air-fuel mixing chamber of the carburetor, and fuel enters the carburetor from the fuel bowl due at least in part to pressure differentials occurring within the venturi region.
Many such engines are used in seasonal machines (e.g., lawnmowers, snow blowers, tillers) or other machines that are not operated for long periods of time (e.g., chain saws), or that are operated under low-temperature conditions. When an engine is cold and/or has not be operated for a long period of time, it can be difficult to start the engine. Additionally, even after the engine has been started, the engine may not run smoothly until the engine warms up. To enhance the performance of such engines under these operational conditions, many engines include an engine priming mechanism by which, to achieve enhanced engine performance, the carburetor is provided with a richer air-fuel mixture.
To prime the carburetor, most carburetors in traditional schemes have a fitting that is pressed or screwed into the carburetor body. The fitting is further connected to passages leading to the fuel bowl attached to the carburetor, with the passages typically being cast or drilled into the carburetor body. Additionally, the primer fitting typically receives at its opposite end (opposite to the end that fits into the carburetor) a primer tube, which can either be directly connected to a primer bulb or lead to another location on the engine at which such a bulb or other priming device is located. More particularly, when a user presses the primer bulb, air is delivered from the priming bulb through the primer tube, the primer fitting and the passages within the carburetor body to the carburetor fuel bowl, and the resulting air pressure increase within the fuel bowl causes fuel to be driven into the carburetor venturi. Depending upon the embodiment, the priming bulb can provide a bowl vent (e.g., by including a small hole within the priming bulb) all by itself or in combination with additional passage(s).
Although adequate in many circumstances, such conventional priming mechanisms nevertheless are inadequate in some regards. In particular, such conventional priming mechanisms involving a primer fitting require assembly of the primer fitting to the carburetor body. As a result, the potential exists for the fitting to slip out of place or crack the carburetor body. Also, many conventional priming mechanisms are not well-suited for allowing engine operation under varying temperature conditions. For example, priming mechanisms utilized in engines that are designed for operation under warm (e.g., summer) conditions often are incompatible with optimal operation of the engines under cold (e.g., winter) conditions, since shielding that is often constructed around the carburetor of an engine to protect it from cold air and snow during operation under the latter conditions can obstruct access to the engine's priming mechanism.
For at least these reasons, therefore, it would be advantageous if an improved priming mechanism could be designed. More particularly, it would be advantageous if, in at least some embodiments, such an improved priming mechanism did not require or employ any separate primer fitting. Also, it would be advantageous if, in at least some embodiments, the priming mechanism was compatible with engine usage under various different temperature (or possibly other) operational conditions.